No problem. The version that came with Flash Builder 4 was the 4.0 release version of FlexUnit. We didn't introduce parameterized testing until the 4.1 beta version. If I run your code (with references to your Rand class commented out) it all works as expected which is why I guessed we were on different versions.

Download the 4.1 RC1 code (which will be released very shortly). You will get a bunch of libraries and docs in the zip file. You can ignore most of that for now. All you really need is the flexunit-core-*.swc file. Extract that one and drop it in the libs folder of your project and your code will likely run just fine.

Great. Just updating that core swc file should take care of everything. You could replace the version FlashBuilder uses directly, or just drop it in the libs folder of your project which will effectively trump the version that comes with Flash Builder.